Web server malware for Nginx, Apache advertised on underground market

A new malware program that functions as a module for the Apache and Nginx Web servers is being sold on cybercrime forums, according to researchers from security firm IntelCrawler.

The malware is called Effusion and according to the sales pitch seen by IntelCrawler, a start-up firm based in Los Angeles that specializes in cybercrime intelligence, it can inject code in real time into websites hosted on the compromised Web servers. By injecting content into a website, attackers can redirect visitors to exploits or launch social engineering attacks.

The Effusion module works with Nginx from version 0.7 up to the latest stable version, 1.4.4, and with Apache running on 32- and 64-bit versions of Linux and FreeBSD. ModulModules extend Apache's and Nginx's core functionality.

The malware can inject rogue code into static content of certain MIME types, including JavaScript and HTML, and in PHP templates at the start, end or after a specific tag. Attackers can push configuration updates and control code modifications remotely.

Filters can also be used to restrict when the injection happens. Effusion supports filtering by referrer header, which can be used to target only visitors that come from specific websites; by User-Agent header, which can be used to target users of specific browsers and by IP address or address range.

The malware can check whether it has root access, something that could allow the attackers greater control over the underlying system. It can also delete the injected content when suspicious processes are detected in order to hide itself, Andrey Komarov, IntelCrawler's CEO, said via email.

The Effusion authors offer precompiled builds for US$2,500 per build and plan to vet buyers, Komarov said. This suggests they're interested in selling it only to a limited number of people so they can continue to offer support and develop the malware at the same time, he said.

While this is not the first malware to function as an Apache module, it is one of the very few so far to also target Nginx, a high-performance Web server that has grown considerably in popularity in recent years.

According to a December Web server survey by Internet services firm Netcraft, Nginx is the third most widely used Web server software after Apache and Microsoft IIS, and has a market share of over 14 percent. Because it's built to handle high numbers of concurrent connections, it is used to host heavily trafficked websites including Netflix, Hulu, Pinterest, CloudFlare, Airbnb, WordPress.com, GitHub and SoundCloud.

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